1. Field of the Invention
The present invention is directed generally toward low current switching devices and, more specifically, to a dual-shielded reed relay for surface mount applications.
2. Description of Related Art
Switching applications commonly use reed relays for connecting or disconnecting selected circuits. Typically, as shown in FIG. 1, a reed-type switch includes a pair of switching contacts 1, 2 that are supported by adjustable switching elements 9 made from a magnetic material. The contacts 1, 2 and their switching elements 9 are surrounded by and actuated by an electrically-magnetized operating coil (not shown). For example, each of the contacts 1, 2 are adjustable, but normally separated from each other in a switching state referred to as “open,” so that the lead 3, 4 associated with each contact 1, 2 of the relay is electrically disconnected from the other. Such a reed-type switch is referred to as being normally open. When the coil is energized, the magnetic field generated urges the switching elements inward, causing the contacts 1, 2 to be placed in contact with each other, thereby electrically connecting the leads 3, 4.
Reed relays are used in low current switching assemblies adapted to connect selected circuits 5 in an equipment testing environment to a signal measurement unit 6. Circuits 5 of a device under test are connected to a switching matrix that includes a plurality of relay assemblies. Test equipment 6 is also connected to the matrix such that selected circuits of the device under test are connectable to selected test equipment inputs by operation of the relays. In such a testing environment, a high degree of accuracy and consistency is desirable in the signals conducted through the relays to achieve accurate test results. But because the currents tend to be very low (on the order of 1×10−15 A), the signals are susceptible to even small amounts of interference and leakage.
Insulation and shielding can reduce interference and leakage. For example, the reed switch in FIG. 1 includes a single copper foil shield 7 that has been connected to one of the switching element leads by a jumper 8 and wrapped around the entire reed-type switch, including both switching element contacts 1, 2. The foil shield 7 is electrically connected to conduct a “guard” signal during testing to minimize the leakage through the contact 2 and its associated lead 4 during testing. However, when the contacts 1, 2 in FIG. 1 are electrically disconnected and form part of a test matrix, leakage can occur through the lead 3 electrically connected to the test measurement unit 6. Moreover, the shield 7 is formed from an electrically conductive material which, when wrapped around the contacts 1, 2 can create a possibility of shorting adjacent on a printed circuit board if the shield makes contact with those traces. This possibility has limited the types of applications in which the relay can be employed because a pin connector is required to be provided to the relay for connecting the relay to printed circuit boards (“PCBs”) and suspending the conductive shield 7 above the PCB to insulate the shield 7 from the traces on the PCB. Additionally, through-pin connectors for mounting electronic components to a PCB is labor intensive, and expensive.
Installing a circuit component with a pin connector on a PCB requires manual insertion of the component onto the board such that the pins are inserted through plated holes. Once properly positioned, solder or other conductive adhesive is used to solder the pins to the plating lining the holes or a pad on the surface of the PCB to permanently affix the component to the PCB. Such pin-connector components not only add to the cost of assembly, but consume significant real estate on the PCB, and require expensive manufacturing and packaging techniques to bring components to market.
Accordingly, there is a need in the art for a reed relay that is surface mountable, yet shielded to minimize current leakage during low-current applications.